It is known to use cationic surfactants in detergent compositions. For example, GB 2040990A describes granular detergent compositions comprising cationic surfactants.
EP-A-121949 also describes cationic surfactants for use in laundry detergent compositions. This reference describes a broad class of cationic surfactants.
The Applicants have found that a particular group of quaternary ammonium cationic surfactants gives good cleaning properties, especially on greasy, oily stains.
The cationic compounds have been found to be particularly beneficial in detergent compositions which additionally comprise anionic surfactants. Without wishing to be bound by theory, the Applicant believes that the particular cationic surfactants used in the detergent compositions of the present invention have surprisingly good solubility. In addition, they form an association in the presence of anionic components to produce surprisingly soluble anionic/cationic complexes which lead to unexpected performance benefits: the cationic surfactant rapidly and effectively contacts greasy stains and rapidly penetrates and breaks down the stain giving effective greasy stain removal. Furthermore, it is believed that following breakdown of the oily soil the cationic surfactants used in the present invention also form complexes with the fatty acids and any other negatively charged breakdown product produced, increasing their solubility and enhancing greasy, oily soil removal and overall cleaning performance.
However, in processing or in use in alkaline detergent conditions, it has been found that some cationic surfactants may produce malodours in the washing liquor. Whilst not wishing to be bound by theory, the Applicants believe that malodours arise due to exchange of the counterion of the cationic surfactant with hydroxide ions in the aqueous alkaline wash liquor. The quaternary ammonium hydroxide product which results may then produce malodorous amine bi-products. In order to avoid this problem in use in alkaline conditions the particular cationic surfactants should have a counterion which has a higher relative selectivity for the cationic surfactant than a hydroxide ion in aqueous solution under the conditions of use.
All documents cited in the present description are incorporated herein by reference.